“When the monkeys heard this, they all covered their faces and wept mournfully, each one troubled by his own impermanence.”

The monkeys who follow the stone monkey join him in worrying that they will be forgotten when they die. They know they are mortal, so their lives will end. They don’t so much fear the process of death as they do its result: removal from existence. They fear being subjected to the whims of Yama, who is the King of the Underworld.

“Nothing in the world is difficult; only the mind makes it so.”

Patriarch is trying to teach Wukong that mind over matter can allow one to accomplish previously presumed impossible feats, such as cloud-soaring. 

“In an orderly fashion, they made the entire Flower-Fruit Mountain as strong as an iron bucket or a city of metal.”

One of the important elements of Daoism is alchemy, so any transformation of one substance to another—such as the transformation of earth (the mountain) into metal (iron)—is a reference to the Daoist arts. Whenever characters fight using the Way, they usually use transformation to gain the competitive edge.